The invention relates to a method of changing rolls in a machine utilizing strip material. In the context of the specification, the "machine" may be taken to mean any type of equipment designed to make use of strip material, and more especially a wrapping machine in which such strip material is utilized for the purpose of enveloping or packaging commodities (i.e., articles).
It is a standard practice, in machines of the type in question, to utilize rolls of strip material arranged in alignment one with the next along a common axis internally of a magazine. The rolls are taken up from the magazine singly and in succession by means of a transfer device and supplied thus to the wrapping machine. The prior art also embraces machines of high output capacity equipped with at least two uncoiling stations, each of which provides a respective uncoiling axis and accommodates one roll. As each roll is depleted, the other uncoiling station comes into operation.
U.S. Pat. No. 4,896,842 discloses the expedient of supplying rolls of strip material to one or other of two uncoiling stations by means of a transfer device comprising a head, capable of taking up one roll, which is carried by the end of an arm mounted pivotably about an axis positioned between the two uncoiling stations and equidistant from their axes.
Due to rocking motion of the arm, the head describes a trajectory coinciding with an arc to a circle that intersects both the axes of the two uncoiling stations and the common axis of the rolls occupying the magazine. Thus, it becomes possible to take up a roll from the magazine by means of the transfer head, and by swinging the arm, to transfer the head together with the roll from the magazine to one or other of the two uncoiling stations.
The conventional transfer device briefly outlined above has certain drawbacks of both structural and operational character, attributable in essence to the movement whereby the head is distanced from the common axis of the rolls occupying the magazine (in effect, the magazine axis) and aligned with the axis of one or other uncoiling station, which is such that the change roll must always describe an arc to a circle. Given the sometimes notable mass and diametral proportions of the rolls of strip material utilized, such a movement requires the application of relatively high driving and braking torques to the arm. Also, the need to accommodate this movement imposes a marked rigidity in general design of the machine. In effect, the machine must always be proportioned in such a way that the axis of rotation of the transfer arm can be positioned equidistant from the axes of the magazine and the uncoiling stations. Again, if one is to minimize both the dimensions of the transfer device as a whole, and the driving/braking torque applied to the arm, then the length of the arm itself must be reduced to a bare minimum by siting its pivot axis exactly mid-way between the axes of the uncoiling stations, indeed equidistant from the two axes in question and occupying a common plane, as disclosed in U.S. Pat. No. 4,896,842.
It will be clear that the conventional transfer device aforementioned not only requires somewhat high powered rotary actuators in order to operate correctly, but is unsuitable in general terms for integration into existing machines given that the geometry of such machines will not correspond in most instances to that expressly required by the device.